Railroad diagrams for the pattern you actually typed

Regex Studio draws a railroad diagram from the expression in the box and highlights matches in the sample text as you type. The diagram is generated here; there is no "explain this regex" API and the corpus never leaves the page.

Use it when you need to show a reviewer what (?=…) or a nested group is doing, or to confirm a pattern against logs you should not paste into a hosted tester. Code snippets for common languages are templates, not an execution environment.

JavaScript regex semantics apply (no Python re.VERBOSE, no lookbehind in engines that lack it). If the pattern is invalid, the diagram stays empty and the error is shown next to the input instead of failing closed with a generic "no matches".

Regular Expression

/ /

g (global) i (insensitive) m (multiline)

Test String 2 matches

Code Snippet

const regex = /([A-Z])w+/g;
const str = '';
let m;

while ((m = regex.exec(str)) !== null) {
    // This is necessary to avoid infinite loops with zero-width matches
    if (m.index === regex.lastIndex) {
        regex.lastIndex++;
    }
    
    // The result can be accessed through the `m`-variable.
    m.forEach((match, groupIndex) => {
        console.log(`Found match, group ${groupIndex}: ${match}`);
    });
}

Visualization

Generating diagram...

Explanation

Match Results

Match #	Full Match	Groups	Index

Character Classes

Pattern	Matches
`\\d`	Any digit (0-9)
`\\w`	Word char (a-z, A-Z, 0-9, _)
`\\s`	Whitespace
`.`	Any char except newline
`[abc]`	Any of a, b, or c
`[^abc]`	Not a, b, or c

Quantifiers

Pattern	Meaning
`*`	0 or more
`+`	1 or more
`?`	0 or 1
`{n}`	Exactly n
`{n,m}`	Between n and m

Anchors & Groups

Pattern	Meaning
`^`	Start of string
`$`	End of string
`(...)`	Capture group
`(?:...)`	Non-capture group
`(?=...)`	Lookahead
`\\b`	Word boundary

Common Patterns

Pattern	Matches
`^[\\w.+-]+@[\\w-]+\\.[\\w.]+$`	Email
`^https?:\/\/`	URL
`^\\d{4}-\\d{2}-\\d{2}$`	Date (YYYY-MM-DD)
`^\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}$`	IPv4

What are Regular Expressions?

Regular expressions (regex) are powerful patterns used to match character combinations in strings. They are essential tools for text processing, validation, and data extraction across programming languages. Regex patterns consist of literal characters and special metacharacters that define search rules. They are used in form validation, log parsing, search and replace operations, and data cleaning tasks.

How to Use This Tool

Enter your regex pattern in the input field. The tool will automatically generate a railroad diagram visualizing the pattern structure. Add test text to see real-time match highlighting and explanations. Use the cheatsheet for quick reference on common patterns and syntax. Generate code snippets for your preferred programming language.

Common Use Cases

Email validation to ensure user input matches proper email format before processing, log parsing to extract timestamps and IP addresses from server logs, data cleaning to remove unwanted characters or format phone numbers consistently, and search and replace for bulk text transformations with pattern matching.

Pro Tips

Start simple and build complex patterns incrementally. Use non-capturing groups (?:) when you do not need to reference the match. Test edge cases like empty strings and special characters. Consider regex readability — complex patterns can be documented with comments.

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